Radio Frequency Identification (RFID) refers to a process of transferring data over a Radio Frequency (RF) signal between a reader and a device that is attached to an item. RFID is commonly used for identifying and tracking items. For example, RFID devices may be attached to items in a warehouse so that inventory in the warehouse may be tracked. The RFID device, also referred to as a RFID tag, typically stores an identifier (ID) for an item in memory. The RFID device reads the item ID from the memory, and broadcasts a RF signal that includes the item ID (e.g., the item ID is modulated on the RF signal). An RFID reader receives the RF signal and interprets the item ID from the RF signal.
Most RFID devices include an antenna that receives and transmits RF signals, and an integrated circuit that stores data and processes the RF signals. Some RFID devices also include a battery, and are referred to as active devices. Other RFID devices do not include a battery, and are referred to as passive devices. In a passive RFID device, the power for the integrated circuit is supplied by a RF signal transmitted by the RFID reader. The antenna in the passive RFID device receives the RF signal from the RFID reader. The antenna has a coiled configuration which causes the RF signal to form an electromagnetic field in the antenna. The integrated circuit derives power from the electromagnetic field, which energizes the integrated circuit instead of a battery or some other power source. With the power supplied by the RF signal, the integrated circuit reads the data stored in memory, and modulates the stored data onto the RF signal. The antenna then transmits or reflects the modulated RF signal for reception by the RFID reader. The RFID reader senses the RF signal from the passive RFID device, and processes the data added to the RF signal.